1. Field of the Invention
This invention relates generally to DC-DC converter control circuits, DC-DC converters, power supply units, and DC-DC converter control methods and more specifically to a technology capable of maintaining a specified voltage relationship existing between the output voltages of DC-DC converters.
2. Description of Related Art
In a power supply unit which is equipped with a plurality of DC-DC converters and which provides a plurality of output voltages, it might be necessary to constantly maintain the relative voltage relationship between power supply voltages. For example, when supplying a power supply voltage Vcc and a high-order backgate voltage VBGP to a PMOS transistor, it is necessary to maintain a voltage relationship so that the power supply voltage Vcc constantly falls below the high-order backgate voltage VBGP in a series of sequences from the time power is turned on to the time power is turned off, the reason for which is to prevent the occurrence of a burnout et cetera due to latch-up.
As the related art of the above, Japanese unexamined patent publication No. 9(1997)-154275 and Japanese unexamined patent publication No. 10(1998)-323026 have been disclosed.